Control system for vapor-deposition coating apparatus



GRBSS REFERENE SERCH R00! 2 Sheets-Sheet 1 G. DYKEMAN ET Al- Af/orneyCONTROL SYSTEM FOR VAPOR-DEPOSITION COATING APPARATUS MTRM XR.;

' Aug. 20, 1968 Filed Nov. l0, 1965 Aug. 20, 1968 G. DYKEMAN ET AL3,397,672

OONTROTJ SYSTEM FOR VAPOR-OEPOSITTON COATTNG APPARATUS Filed Nov. lO,1965 2 Sheets-Sheet' T;

MODI .max v 1i ma?. Il MNM INVENTORS GEORGE DYKEMA/V and FRAN/(L/WA lAfforney @H TME' United States .ABSTRACT OF THE DISCLOSURE A pluralityof electron guns spaced across the width of a strip traveling through avacuum chamber, serving to vaporize coating metal in a crucible, areControlled in response to the speed Vof the strip and the thickness ofthe deposited coating, to maintain the latter uniform. A differential ismaintained between the guns adjacent the strip edges and those nearerthe center line, to obtain uniform deposition transversely of the strip.A second series of guns used for preliminarily degassing the strip, iscontrolled in accordance with the temperature of strip entering thechamber, to insure proper heating and release of occluded gases.

This invention relates to a control system for adjusting the severalconditions involved in the continuous coating of strip material in avacuum, by deposition of -metal vapor thereon, according to the speed oftravel of the strip. More particularly, it relates to a system forcontrolling the evolution of vapor from the surfaces of molten pools ofthe coating metal to insure a substantially uniform thickness of coatingboth transversely and longitudinally of strip.

'BACKGROUND OF THE INVENTION In the vapor-deposition coating ofcontinuous strip material, .it is desirable to arrange an elongatecrucible transversely of the strip travel and to heat the top surface ofa charge of coating metal therein. This may conveniently be done byelectron bombardment using a plurality of so-Called electron guns(emitters) positioned alongside the crucible and disposed end-to-endrelative to each other. The paths of the electron beams from the guns tothe surface of the metal in the Crucible are controlled by vmagneticelds transverse to the beams, as shown in Simons U.S. Patent No.3,046,936. It is also desirable to use severa-l of these crucible-gunarrange-ments spaced along the path of the strip when thick coatings aredesired. It is the object of our invention to control both the totalpower applied to the surface of the metal in the crucible and thedistribution of power among the several guns to provide a pre-selectedcurve of rate of metal vaporization along the length of the crucible(i.e., transversely of the strip), and to control the rate of supplyingmake-up metal to the crucibles in accordance with strip speed and toproduce on the strip a coating of uniform thickness longitudinally andtransversely thereof.

lBeam power as used herein is the power delivered to the surface of themetal in the crucible by an individual electron-beam gun. A selectedbeam power Imay be achieved at either a relatively high voltage and lowlevel of beam-current or vice versa. The use of electron guns as heatingsources in high-vacuum continuous processes involves the resolution ofconflicting sets of operating characteristics. For example, linearcontrol of power is desirable but an electron gun is basically anonlinear device. Again, uninterrupted flow of power is desirable butionization discharges occur frequently due to impurities brought in bythe process materials causing momentary short circuits to the powersupply. Wide-range power arent 3,397,672 Patented ug. 20, 1968 SUMMARYOF THE INVENTION It is an object of this invention to control amultitude of simple electron guns so as to obtain uniform heating of aCrucible much larger than an individual electron-gun source. Accordingto our invention, the beam-power and filament-heating circuits of thegun are interconnected so as to maintain total power distributionaccording to preselected references and vary the total power as requiredby process variations and thus tov maintain preselected heating of acrucible or of the continuous strip material itself.

For this purpose, the electron-beam guns must be operated withincontrolled voltage, beam-current and filament-current (temperature)ranges. For example, if the filament (emitter) temperature issufficiently high to make available more electrons than can be attractedto the crucible metal at maximum voltage (emission limited), beam powermay be altered by varying the voltage. Second, if the voltage issufficient to attract from the filament to the metal in the Crucible themaximum quantity of electrons the lament can emit (temperature limited),then power density may be contr-olled by varying filament current(temperature). Furthermore, if the filament is temperature limited andthe voltage is below maxim-um, beam power may be controlled by varyingboth filament temperature and voltage until either the first or secondcondition described above is achieved.

BRIEF yDESCRIPTION OF THE DRAWINGS A complete understanding of theinvention may be obtained from the following -detailed description andexplanation which refer to the accompanying drawings illustrating thepresent preferred embodiment.'

In the drawings:

FIGURE 1 is a diagrammatic showing of vapor-deposition coating apparatusand partial circuit diagram of the control system of our invention; and

FIGURE la is the remainder of the control-system diagram.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now in detail to thedrawings and, for the present, particularly `to FIGURE l, the apparatuswith which our invention is adapted to be used comprises a vacuumChamber 10 having entrance and exit roll seals 11 and 12. `Chamber 10 isevacuated by suitable pumps (not shown) to a low pressure such as .O2-.1micron of mercury. Guide rolls 13 in the chamber cause strip 14 passingtherethrough to trav-el first beside electron-beam gun preheaters 15 andthen in reverse directions over pairs of elongated transversely disposed.refractory crucibles 17 and 18 for coating both sides thereof. Groupsof electron-beam guns 19 (such as the Model 60-850 gun made `by UltekCorporation, Pal-o Alto, Calif.) extend end-toend along each crucibleand electromagnets 20 are mounted on appropriate core structures toprovide fields for maintaining the desired curvature of the -beams asaforesaid. Wire-feed apparatus 21 for each crucible supplies make-upcoating metal, e.g., aluminum, from storage 16. A surface pyrometer 22(such as Model TD-3, made lby Radiation Electronics Company, Chicago,Ill.) measures the temperature of the strip after preheating and coatingthickness gages 23 (such as the Quantrol Analyzer made by AppliedResearch Laboratories, Inc., Glendale, Calif.) measure the thickness ofthe coating applied to one side `of the strip. A tachometer generator 24generates a voltage proportional to the speed of strip traversingcharnber 10 and this voltage applies a signal to a master controller 25now to be described.

The system of our invention is responsive to a master control, theelements of which, enclosed within dotted rectangle 25, hereinafterdesignated a controller, include potentiometers 26, 27 and 28 which areadjusted automatically to give the wire-feed rate, gun filament currentand gun-power input, respectively, suitable for depositing the desiredweight of coating on the strip for a given speed of travel thereof.

FIGURE la shows the control system for the filaments 29A, 29B, etc., ofthe group of five electron guns disposed end-to-end, associated with oneof the crucibles 17, as indicated at 19. Each crucible has a similar setof guns. The electron-beam power input to each set of guns is obtainedfrom a primary source 30, through a three-phase saturable-core reactor31 (commercially available from electrical manufacturers such as GeneralElectric Company), a transformer 32 and rectifiers 33 (such as thesilicon rectifier made by Westinghouse Electric Corporation), whichprovide a high direct voltage (5,000-15,() v.) across buses 34 and 35,the positive of which (35) is grounded. The power input drawn from thesebuses is measured by a wattmeter 36 (such as Weston Instruments Modell483) delivering a signal voltage which is opposed lby that frompotentiometer 28, through a resistance network (to be described indetail later) the difference being applied to a power -amplier 37 (suchas that made by Norbatrol Electronics Corporation, Pittsburgh, Pa.). Theoutput from the amplifier energizes the field winding of an excitergenerator 38 driven by a constant-speed motor (not shown). Generator 38energizes the several control windings 31A of reactor 31. The result isa closedloop control Acircuit whereby the reactor is energized tomaintain a constant power input by correcting the `applied voltageaccording to the setting of potentiometer 28, depending, however, uponother variable conditions as will be explained subsequently.

The filaments 29A, 29B, etc. of the electron-beam guns are connected toa supply of heating current through transformers 39A, 39B, etc., underthe control of magnetic amplifiers 40A, 40B, etc., similar to `amplifier37, which are themselves -connected to the A-C power supply. Each ofthese amplifiers has a control winding 41A, 41B, etc. connected to a bus42 from an amplifier 43. Amplifier 43 is connected to and derives itsinput from filament-control potentiometer 27 through a resistancenetwork (to be described in detail later), and a voltage tapped from bus34 by a voltage-divider network 44 -including a Zener diode 45 (such asthat made by International Rectifier Corporation) a local source 46 ofbias voltage and `a manually set potentiometer 47. Accordingly, thecurrent supplied to all filaments 29A, 29B, etc. is controlled by thedifference between the voltage from potentiometer 27 and that fromnetwork 44. Potentiometer 47 governs the proportionality between thevoltage tapped from bus 34 and that from potentiometer 27. Network 44modifies the input to amplifier 43 only if the voltage on bus 34 isabove or below a desired operating range fixed by the selection of theZener diode 45 and the setting of a potentiometer 48 controlling theapplication of bias voltage thereto.

Amplifiers 40A, 40B, etc. also have control windings 49A, 49B, etc.energized in accordance with the individual filament-currents, as byshunts 50A, 50B, etc. Individual control of the heating currents to theseveral filaments is effected by transductors 51A, 51B, etc. Thetransductors are magnetic amplifiers (such as the direct-currenttransformers made by Magnetic Controls Company, Minneapolis, Minn.)connected to an A-C power source and receiving individual input currentsignals from high-voltage bus 34, and are connected to the filamentsindividually. Thus the direct-current outputs of the -transductors, ie.,isolated signals proportional to the high-voltage supply currents to theseveral filaments, are yalso applied to magnetic amplifiers 40A, 40B,etc., to regulate filament temperatures and maintain the -proper.relation thereof to the density of electron-beam discharge from thefilaments to the crucible.

We provide means for maintaining a marginal excess in the beam-currentsfrom the outer guns over that from the inner guns, to improve theuniformity of the coating thickness transversely of the strip. Thismeans includes further control windings 52A, 52B, 52D and 52E onamplifiers 40A, 40B, 40D and 40E, respectively. There is no such windingon amplifier 40C. These windings are energized by the outputs oftransductors 51A, 51B, 51D and 51E, respectively. By potentiometers 52and 53, which are mechanically coupled, transductors 51A and 51E are setto energize filaments 29A and 29E at a higher level than that offilaments 29B, 29C and 29D the transductors 51B, 51C and 51D of whichall operate at the same level by virtue of their common connection 54.Since transductor 51C does not affect amplifier 40C, the latterenergizes filament 29C at a minimum level. Amplifiers 40B and 40Denergize filaments 29B and 29D at a higher level and amplifiers 40A and40E energize filaments 29A and 29E at a still higher level. Thisproduces an increasing evaporation rate from the center of Crucible 17toward each end, and thereby offsets the decrease in coating thicknessad` jacent the strip edges which would otherwise result.

A second control function exercised by controller 25 is to determinesuitable power distribution among the sevn eral successive crucibles 17,17. It is usually desirable to proportion the power equally among theseveral crucibles used, although it is recognized that special advantagecan be taken of the nonlinear relationship between power and evaporationrate by proportioning the power in a different manner. To effect thedesired division of power between the gun-control systems of two or morecrucibles, a multiple-contact switch 72 is used to select resistors 73,74 which divide the reference signal by one, one-half, or one-third,depending on whether one, two, or three crucibles are in use. As shownin FIGURE la, either the first or the third may be used alone, the firstand second used together, or all three used together. Additional networkconfigurations would permit other combinations. Since the signaldividing resistors 73 and 74 are adjustable, various proportions can beset, i.e., all three crucibles could be operated on 100% power referencesignal.

A third control function exercised by controller 25 is to vary the rateat which wire-feed mechanism 21 operates. For this purpose, acontroller` 55 (such as Type C Basic Electronic Governor made by LindeDiv., Union Carbide Corporation) varies the speed of motor 56 drivingwire-feed pinch rolls 57. Controller 55 responds to the differencebetween the voltage from poten`1 tiometer 26 and that produced by atachometer generator 58 coupled to motor 56.

The several potentiometers 26, 27 and 28 of controller 25 are driven inunison by a servo 59 (such as Model 6102 made by Solar ElectronicsCompany, Hollywood, Calif), in accord with variations in thickness ofcoating deposited on strip S from the desired value, and variations instrip speed. Signals of thickness variations ob served by gage 23 aresupplied to an intermediate servo 60 (similar to servo 59) mechanicallycoupled to a potentiometer 61 which applies a voltage to servo 59.Potentiometer 61 is connected in a bias-voltage network 62 whichreceives input from potentiometers y63 and 64 for introducing theretovoltages corresponding to preselected strip widths and coatingthicknesses, respectively.

A strip-speed measurement is taken from tachometer generator 24. Thevoltage from generator 24 is applied to potentiometers 63 and 64 andthus combines with the preset width and coating-thickness adjustments toaffect network 62. Timer 65 (to be described in detail below) causes aperiodic adjustment of potentiometer 61, if needed, by servo 460, andpotentiometer 61 affects servo 59. Servo 59 in turn actuatespotentiometers 26, 27 and 28 with the results already explained.

Timer 65 affects resetting of controller 25 in accord with the thicknessof coating measured by gage 23 at a rate which varies with the stripspeed thus compensating the delay between thickness measurement andcontroller re-adjustment for the time required for a point on the stripto travel from the crucibles 17 to the gage. The timer is a two-periodsequencing timer such as that made by Square D Co., Milwaukee, Wis., andcontrols the operation of servo 60. One period (the on period) of thetimer is determined by the setting of a rheostat 65C. The other period(the off period) is controlled by a variable resistor 65D. This resistoris a photocell the resistance of which is controlled by the light from alamp 65E energized by Voltage from tachometer generator 24. Thephotocell 65D and lamp 65E form a combination provided in thecommercially available Raysistor electrooptical device made by RaytheonCo., Newton, Mass.

Contacts 66 of timer 65 are closed during the on period and open duringthe off period. Rheostat 65C is initially adjusted to make the on periodsuicient to correct for a 100% error signal input to servo 60. As stripspeed increases lamp 65E glows more brightly, reducing the resistance ofphotocell 65D and, consequently, the length of the off periods of timer65. As operation of the system is c-ontinued rheostat `65C may beadjusted to reduce the length of the on periods and thus shorten thetimes for operation of servo 60.

If the actual coating weight as measured by gage 23 is the same as thedesired coating Weight according to which potentiometer 64 is set, theinput to servo 59 will be determined by potentiometers 63 and 64. If theactual coating weight differs, the action of servo 60, timer 65 and thebias-voltage network 62 serve to increase or decrease the signal appliedto servo 59 in proportion to this difference. Servo 59 proportionallyincreases or decreases the setting of lpotentiometers 26, 27 and 28 toadjust the entire control system to a level that will provide thedesired coating thickness. Since the coating operations and thethickness measurement are necessarily separated in space, the delaybetween coating and measurement is made proportional to line speed. Asexplained above, timer 65 effects the delay between corrections to servo59 by servo 60, so as to make the delay proportional to line speed.

The current supply to the winding of electromagnet 20 is controlled by acurrent regulator 67 (as an example, see application brief dated May 17,1963, published by George A. Philbrick Researchers, Inc., Boston, Mass.)according to the input voltage of wattmeter 36 applied to apotentiometer 68.

It is to be understood, of course, that the control systern describedabove is intended for the electron-beam guns of one crucible and isduplicated for the guns of each of the other crucibles.

One feature of our invention remaining to be described is the control ofthe preheating electron guns 15. This in cludes a power supply 69(comprising units similar to 31, 32 and 33), a filament-control circuit70 (duplicating all units designated by numerals 39 through 54 with andwithout reference letters added) and a master control 71 similar to thatindicated at 25 except that, instead of coating thickness, thetemperature of the strip as noted by pyrometer 22, governs theoperation, after predetermined settings for strip width, strip thicknessand desired temperature have been established on potentiometers similarto those shown at 63 and 64. It will be under- Cit stood from the abovethat, not only the energization of the filaments of vaporizing guns 19increases from the midpoint of the crucible toward each strip edge, butalso the energization of the filaments of preheating guns 15 issimilarly increased.

It will be evident from the foregoing that our invention ischaracterized by numerous advantages. In the first place, the system maybe set up in advance for a specific desired coating thickness to beapplied to strip of a certain width at a given speed of travel. Thefilament-current needed for thesemconditions, the voltage appliedbetween filament and crucible and the power input to the electron gunswill be maintained at the proper values or adjusted as `necessary toassure the desired result, i.e. uniform coating thickness`over the striparea, despite such possible changes in strip speed or coating thicknessactually applied as may occur for various reasons. The preheating of thestrip and the rate of deposition of the coating metal, furthermore,tendto decrease from the center line of the strip toward the edges.Therefore, to secure a substantially uniform heating or coating acrossthe width compensation for this effect must be made. The desireddistribution of preheating or vaporizing energy is maintained despitechanges in the overall level of energy input. The system maintainssuitable power input to the guns by varying the voltage or current orboth as needed to suit variations in the controlling parameters.

Although we have disclosed herein the preferred embodiment of ourinvention, we intend to cover as well any change or modification thereinwhich may be made without departing from the spirit and scope of theinvention as set forth in theA claims.

We claim:

1. In apparatus for coating traveling strip with metal by vapordeposition in a vacuum, the combination with a crucible adjacent thepath of the strip adapted to contain coating metal, an electron gunadjacent the crucible having a thermionic emitter and delivering a beamof electrons to the metal therein, of means for supplying electric powerto said gun, said means including voltage-control means, and meansresponsive to the speed of the strip effective to vary saidvoltage-control means.

2. Apparatus as defined in claim 1 characterized by means varying thecurrent from said power-supply means to the emitter of said gun and saidspeed-responsive means including means to vary said emitter-currentvarying means.

3. Apparatus as defined in claim 2 characterized by means modifying theaction of said current-varying means according to the voltage applied tothe emitter.

4. Apparatus as defined in claim 1 characterized by means feedingmake-up metal to said crucible and said speed-responsive means includingmeans varying the speed of said make-up metal feeding means.

5. Apparatus as defined in claim 1 characterized by an electro-magnetadjacent said crucible to deflect said beam and means responsive to thevoltage of said power-supply means controlling the excitation of saidmagnet.

6. Apparatus as defined in claim 1 characterized by said gun including aplurality of thermionic emitters spaced across the width of the stripand means varying the current supplied to the emitters adjacent thestrip edges relative to that supplied to the emitters nearer the centerline of the strip.

7. In an apparatus for coating traveling strip by vapor deposition in avacuum, the combination with a crucible for holding coating metal,disposed across the strip path, a plurality yof electron emitters spacedalong the crucible to bombard the coating metal therein, of asaturable-core reactor having a control Winding varying the powersupplied to said emitters, means comparing the power supplied with apreset standard, and means controlled by said comparing means varyingthe energization of said control f Winding.

8. In an apparatus for coating traveling strip by vapor deposition in avacuum, the combination with a Crucible for holding coating metal,disposed across the strip path, a plurality of electron emitters spacedalong the Crucible to bombard the coating metal therein, of means forsupplying power to said emitters including a magnetic amplier for eachemitter having a control Winding, a transductor for each emitterenergizing the control Winding of the emitters amplifier and meansestablishing the voltage of the emitters at a substantial negative valuerelative to said Crucible, each transductor being connected between itsemitter and said last-mentioned means.

9. Apparatus as dened in claim 8, characterized by each magneticamplifier also having a control winding and means energizing it inaccord with the current supplied by the amplifier to its emitter.

10. Apparatus as defined in claim 8, characterized by means energizingthe transductors of the emitters adjacent the edges of said path toeiect energization thereof at a level higher than that of the remainingemitters.

References Cited UNITED STATES PATENTS Alexander et al. 11S-49.1 XSteigerwald 11S-49.1 X Stein 11S- 49.1 X Alexander 11S-49.1 X Scatchard11S-49.1 X

Samuelson 219-121 Swartz et al 1l8-49.1 X

Hanks 219-121 Cauley Z50-49.5 Dietrich 219-121 X Abraham 219-121 Cauley117-107.1 X Muller 11S-49.1 X Schleich 219-121 Ullery 219--127 MORRISKAPLAN, Primary Examiner'.

